In conventional BIB beverage dispensers, for example, as described in Japanese Patent Laid-Open No. 211299/1994, a beverage material-supplying opaque tube extending from BIB is squeezed by a tube pump (a peristaltic pump) to draw the beverage material from BIB and then to extrude the beverage material via the beverage material-supplying tube to a nozzle, and, at the nozzle, is mechanically mixed with cooled water for dilution or cooled carbonated water.
According to these conventional beverage dispensers, when the BIB has become empty, that is, when the beverage material within the BIB has been sold out, the contemplated beverage no longer can be provided. Therefore, in this case, the empty BIB should be replaced with new BIB filled with the beverage material. In order to learn the sold-out of the beverage material within the BIB, a detector for sensing the sold-out state has hitherto been mounted in intimate contact with the beverage material-supplying tube. This detector senses, through an electrical factor, such as a magnetic field or an electrostatic capacitance, whether or not the beverage material is present or absent in the beverage material-supplying tube. A sensor in the detector outputs an analog signal as shown in FIG. 8.
FIG. 8 shows a change in an analog voltage output from the sensor over a period involving a change in the state of the beverage dispenser from a stand-by state to a beverage selling state. When the degree of a lowering (a difference) in the voltage output from the sensor has exceeded a predetermined threshold value, the detector decides that the beverage material has been sold out. In this case, the detector changes its output to indicate the sold-out state. The dispenser executes sold-out display and the like based on the change in output from the detector.
Since, however, the beverage material-supplying tube is squeezed by the pump, the occurrence of pulsation in the analog signal from the sensor is unavoidable as shown by large waves such as W.sub.1, W.sub.2, W.sub.3 . . . rather than fine waves during selling (on sale) shown in FIG. 8. The straight solid lines L.sub.A and L.sub.B in FIG.8 will be explained later in the preferred embodiment. For this reason, in the prior art, the signal change derived from the pulsation has often been erroneously regarded as a signal change derived from sold-out, leading to malfunction of the beverage dispenser.
In particular, as compared with low-viscosity beverage materials for teas and the like, in the case of high-viscosity beverage materials, for example, for orange juice, a change in analog signal created upon a change in the beverage dispenser from the selling state to the sold-out state is very small. Therefore, despite the fact that the beverage material is still present in the beverage material-supplying tube, there is a great fear of causing an erroneous decision to the effect that the beverage material has been sold out. Conversely, despite the fact that the beverage material has been sold out, there is a great fear of not making a decision to the effect that the beverage material has been sold out.